When growing crops in a field, it is important to kill or control the growth of undesirable plants (weeds) in the field. If not controlled, the weeds compete with crop plants for essential resources such as soil nutrients, water and sunlight. By removing a fraction of these resources or otherwise reducing the availability of these resources to crop plants, the weeds therefore restrict crop growth, resulting in loss of crop yield. Uncontrolled weeds can also have other deleterious effects; for example, weeds present during important operations in the growing of a crop, such as harvest of the crop, can impede these operations, thereby increasing the cost of production.
Timely and judicious use of herbicides can provide the required degree of weed control to avoid crop losses and minimize production costs. Herbicides such as glyphosate or glufosinate that are effective when deposited on foliage of weeds are applied, typically by spraying, post-emergence of the weeds. These herbicides have broad spectrum, that is, they are effective at commercial use rates in controlling a wide range of weed species. They are also very damaging to crop plants if deposited on foliage of these crop plants, except where the crop plants are of a variety selected, whether through traditional breeding methods or through use of genetic transformation technology, to tolerate glyphosate or glufosinate without significant injury. However, glyphosate and glufosinate can generally be used safely in a field where crop plants, even those not tolerant of foliar applications of these herbicides, have not yet emerged as seedlings from the soil. Thus a common method of use of glyphosate or glufosinate herbicides is "pre-plant" application, i.e., before planting of a crop, or "at-planting" application, i.e., immediately before, during or after planting but before emergence of the crop, to weeds that have already emerged.
Weeds tend to emerge over an extended period of time during the early part of a crop growing season. A single pre-plant or at-planting application of glyphosate or glufosinate does nothing to control weeds that have not yet emerged at the time of application, as these herbicides typically have substantially no residual action in the soil at the rates commercially used. It has therefore been known to combine, in a single spraying operation, application of one of these foliar-acting herbicides with application of one or more soil-acting residual herbicides to control weeds that would otherwise emerge after application. Such residual herbicides preferably have sufficient duration of residual activity to control weed emergence up to the time where the crop itself is sufficiently vigorous and has developed a sufficient canopy to suppress the growth of late-emerging weeds. The combination of foliar-acting and residual herbicides has been applied as a tank mixture, i.e., by admixing two or more concentrate compositions, each containing at least one active ingredient, with a suitable volume of water in the tank of a sprayer before application.
Particularly where the crop being grown is corn (maize), tank mixtures of a foliar-acting herbicide with either or both of a residual herbicide of the chloroacetamide class and/or a residual herbicide of the triazine class are known. For example, Harness.RTM. Xtra 5.6L herbicide of Monsanto Company, which contains as active ingredients the chloroacetamide herbicide acetochlor and the triazine herbicide atrazine, is labelled by the manufacturer for use in tank mixture with Roundup.RTM. herbicide of Monsanto Company, which contains as active ingredient the foliar-acting herbicide glyphosate in the form of its isopropylammonium salt. Likewise, Roundup.RTM. Ultra herbicide of Monsanto Company, which contains as active ingredient the foliar-acting herbicide glyphosate in the form of its isopropylammonium salt, is labelled by the manufacturer for use in tank mixture with each of the following: atrazine; Bicep.RTM. and Bicep.RTM. II herbicides of Novartis, which contain as active ingredients atrazine and the chloroacetamide herbicide metolachlor; Bladex.RTM. herbicide of American Cyanamid, which contains as active ingredient the triazine herbicide cyanazine; Bullet.RTM. and Lariat.RTM. herbicides of Monsanto Company, which contain as active ingredients the chloroacetamide herbicide alachlor and atrazine; Dual.RTM. and Dual.RTM. II herbicides of Novartis, which contain as active ingredient metolachlor; Extrazine.RTM. herbicide of Du Pont, which contains as active ingredients atrazine and cyanazine; Frontier.RTM. herbicide of BASF, which contains as active ingredient the chloroacetamide herbicide dimethenamid; Guardsman.RTM. herbicide of BASF, which contains as active ingredients dimethenamid and atrazine; Harness.RTM. herbicide of Monsanto Company and Surpass.RTM. and TopNotch.RTM. herbicides of Zeneca, which contain as active ingredient acetochlor; Harness.RTM. Xtra and Harness.RTM. Xtra 5.6L herbicides of Monsanto Company and Surpass.RTM. 100 herbicide of Zeneca, which contain as active ingredients acetochlor and atrazine; Lasso.RTM., Micro- Tech.RTM. and Partner.RTM. herbicides of Monsanto Company, which contain as active ingredient alachlor; and the triazine herbicide simazine.
In general, chloroacetamide herbicides have deficiencies in their weed spectrum, especially among broadleaf (dicotyledonous) weed species, which can be ameliorated by inclusion of a triazine herbicide in the mixture.
Although tank mixtures of a broad-spectrum foliar-acting herbicide, a chloroacetamide herbicide and a triazine herbicide give satisfactory weed control performance, a need exists for a concentrate herbicidal composition containing all three of these ingredients in suitable amounts relative to each other. Such a composition would require only to be diluted in water to be ready for application, avoiding the need for tank mixing and the problems attendant therewith. In particular, a need exists for a liquid concentrate herbicidal composition that can readily be poured and metered by volume.
Concentrate compositions containing a plurality of active ingredients are typically difficult to formulate because of differing physical properties of the various ingredients and, in some cases, physical and/or chemical incompatibility of the ingredients. Difficulties in formulation are compounded when, as in the case of most commercial herbicide products, the composition must show acceptable storage stability for a period of at least about 30 days, preferably at least about 6 months, under normal storage conditions. Achieving such storage stability is especially difficult where a first active ingredient (e.g., a salt of glyphosate) is highly water-soluble, a second active ingredient (e.g., acetochlor) is liquid at ambient temperature and of very low solubility in water, and a third active ingredient (e.g., atrazine) is solid at ambient temperature and of low solubility both in water and in suitable organic solvents, including the second, liquid, active ingredient.
U.S. Pat. No. 4,075,002 to Drewe et al. discloses herbicidal compositions comprising a solid particulate herbicide, for example a triazine such as atrazine, simazine or ametryn, dispersed in an aqueous solution of a bipyridylium salt herbicide, for example paraquat dichloride.
European Patent Application No. 0 268 574 ('574) discloses herbicidal compositions comprising an aqueous medium having dissolved therein a water-soluble salt of glyphosate and having dispersed therein two substantially water-insoluble active ingredients, namely simazine and diuron, each in solid particulate form. Also present in the disclosed compositions are a first surfactant which is a phosphate ester of an ethoxylated aralkylated phenol and a second surfactant which is an ethoxylated C.sub.8-18 alkanoyl ester of sorbitan and/or an ethoxylated C.sub.14-20 alcohol, together with a thickener.
European Patent Application No. 0 343 142 discloses herbicidal compositions similar to those of '574 except that the first surfactant is a propylene oxide/ethylene oxide block copolymer, the second surfactant is an ethoxylated C.sub.8-18 alkanoyl ester of sorbitan, and a third surfactant is also present, being an ethoxylated fatty amine.
U.S. Pat. No. 5,152,823 to Albrecht et al. discloses aqueous herbicidal compositions comprising at least one water-soluble herbicide such as a salt of glyphosate or glufosinate and at least two herbicides present in disperse form, for example a triazine herbicide (e.g., atrazine, cyanazine, simazine) and a urea herbicide (e.g., diuron, chlortoluron, isoproturon, monolinuron, linuron). Surfactants present in the disclosed compositions include alkyl ether sulfates combined with ethoxylated fatty alcohols and sulfosuccinic monoesters.
U.S. Pat. No. 4,936,901 to Surgant et al. discloses solid water-dispersible granular herbicidal compositions comprising an encapsulated herbicide and at least one non-encapsulated herbicide. The encapsulated herbicide is exemplified by the chloroacetamide herbicide alachlor, and the non-encapsulated herbicide by the triazine herbicide atrazine or by a salt of glyphosate.
A form of liquid concentrate composition that has been used or advocated for herbicidal products, including those containing more than one active ingredient, is a suspoemulsion. The principles of preparing suspoemulsions have been described in the literature, for example by Mulqueen, P. J. et al.: "Suspension emulsions--a new look at tank mix technology in one pack", Pesticide Science and Biotechnology, 273-278 (1987) London: Blackwell; Mulqueen, P. J. et al.: "Recent developments in suspoemulsions", Pesticide Science 29, 451-465 (1990); Seaman, D.: "Trends in the formulation of pesticides--an overview", Pesticide Science 29, 437-449 (1990); Tadros, T. F.: "Disperse systems in pesticidal formulations", Advances in Colloid and Interface Science 32, 205-234 (1990); Tadros, T. F.: "Dispersions and dispersible systems", Proceedings, 8th International Congress of Pesticide Chemistry, 76-86 (1995); Winkle, J. R.: "Suspoemulsion technology and trends", Pesticide Formulation Adjuvant Technology, 175-185 (1996) Boca Raton: CRC; and Memula, S. et al.: "Suspoemulsions with improved stability and correlation of long term stability with the zeta potential", Pesticide Formulations and Application Systems 15, 132-144 (1996).
U.S. Pat. No. 5,362,707 to Fiard et al. discloses a herbicidal suspoemulsion composition comprising a solid particulate herbicide such as atrazine, and containing a sucroglyceride surfactant as an emulifying and/or dispersing agent. No oil-soluble herbicide is disclosed to be present in the oil phase, and no water-soluble herbicide is disclosed to be present in the aqueous phase.
U.S. Pat. No. 5,206,021 to Dookhith et al. discloses stable oil-in-water emulsions containing pesticidal substances such as herbicides in both oil and aqueous phases. It is further disclosed that suspoemulsions can be prepared from such emulsions by addition of a solid pesticidal substance. The compositions disclosed contain a dispersing or stabilizing agent based on titanium dioxide.
U.S. Pat. No. 5,074,905 to Frisch et al. discloses suspoemulsion compositions containing two active ingredients such as herbicides, one in the organic or oil phase and one in the solid particulate phase. It is suggested that "in princuple, water-soluble active ingredients may also be dissolved in the aqueous phase". The disclosed compositions contain an ethylene oxide/propylene oxide block copolymer in the organic phase.
U.S. Pat. No. 4,931,086 to Moucharafieh discloses a herbicidal composition prepared by mixing an oil phase that comprises a liquid thiolcarbamate herbicide and an aqueous phase wherein is suspended a solid particulate triazine herbicide. Also present are an anionic emulsifier that is a calcium alkylbenzene sulfonate, a nonionic or modified nonionic emulsifier of defined formula, a water-soluble wetting agent that is a polyoxyethylene alkylphenol, a first dispersing agent that is a calcium lignin sulfonate, a second dispersing agent that is fumed silica, and an anti-foaming agent. No water-soluble herbicide is disclosed to be present in the aqueous phase.
U.S. Pat. No. 4,826,863 to Szego et al. discloses a suspoemulsion composition in which a water-insoluble active ingredient such as a herbicide is suspended. No herbicides are disclosed to be present in the oil phase or in solution in the aqueous phase.
European Patent Application No. 0 503 989 discloses a herbicidal composition described as a suspoemulsion having a solid particulate phase comprising for example a triazine herbicide such as atrazine, simazine or ametryn. The oil phase comprises sucroglyceride surfactants but no herbicide is disclosed to be present in the oil phase. No water-soluble herbicide is disclosed to be present in the aqueous phase.
Japanese Patent Application No. 06092801 appears from Derwent Abstracts 94-147814 to disclose an aqueous "suspension-emulsion" herbicidal composition comprising a herbicide of low water solubility that is liquid at ambient temperature and is dispersed in the aqueous phase in the form of a microemulsion, and a herbicide of low water solubility that is solid at ambient temperature and is dispersed in solid particulate form in the composition. The composition contains surfactants including calcium dodecylbenzene sulfonate, ethoxylated styrylphenyl ether and ethoxylated castor oil, and a "thixotropic agent" such as ammonium bentonite or finely particulate silica or aluminum oxide. No water-soluble herbicide appears to be disclosed as being present in the aqueous phase.
Chinese Patent Application No. 1076077 appears from Chemnical Abstracts 120:238296 to disclose an aqueous suspoemulsion comprising acetochlor and a "symtriazine" herbicide that further contains emulsifiers, dispersing agents, specific gravity adjusting agents such as isopropanol, thickeners, stabilizers, permeating agents and frost-preventing agents. No water-soluble herbicide appears to be disclosed as being present in the aqueous phase.
That preparation of a stable liquid concentrate three-phase composition containing herbicidal active ingredients in each of the three phases is not a simple matter can be demonstrated by mixing together commonly-used commercial formulations of the various ingredients in the desired proportions. For example, a three-phase composition containing 6% glyphosate, 22% acetochlor and 16% atrazine can be prepared by thoroughly homogenizing, with the appropriate amount of water, Roundup.RTM. Ultra herbicide of Monsanto Company (a formulation of glyphosate isopropylammonium salt), Harness.RTM. EC herbicide of Monsanto Company (a formulation of acetochlor) and a commercial aqueous suspension formulation of atrazine in the appropriate proportions. This composition shows serious formulation instability, as evidenced within 24 hours by flocculation of the atrazine particles and separation of an aqueous phase and oil phase. Similar problems arise if Roundup(.RTM.) Ultra herbicide is thoroughly homogenized with Harness.RTM. Xtra herbicide of Monsanto Company (a formulation of acetochlor and atrazine).